The present disclosure relates generally to an arrangement for, and a method of, trapping debris in an electro-optical reader for reading targets and, more particularly, to preventing any debris formed during the installation of an optical assembly in a chassis of the reader from migrating to optical surfaces of the reader, thereby degrading reader performance.
Moving laser beam readers or laser scanners, as well as solid-state imaging systems or imaging readers, have both long been used, in both handheld and hands-free modes of operation, in many industries, such as retail, manufacturing, warehousing, distribution, postal, transportation, logistics, etc., to electro-optically read targets, such as one- or two-dimensional bar code symbols to be decoded.
The known moving laser beam reader generally includes a data capture assembly or laser scan engine for electro-optically capturing data from a target. The data capture assembly includes a laser for emitting a laser beam, an optical assembly for focusing the laser beam to form a beam spot, a mirrored scan component for repetitively scanning the beam spot across the target in a scan pattern, a photodetector for detecting return light reflected and/or scattered from the target and for converting the detected light into an analog electrical signal, and signal processing circuitry including a digitizer for digitizing the analog signal, and a microprocessor or controller for decoding the digitized signal based upon a specific symbology used for the target to identify the target, and for transmitting the decoded signal, either via a wireless or wired link, to a remote host for further processing, e.g., price retrieval from a price database to obtain a price for the identified target.
The known imaging reader generally includes a data capture assembly or imaging scan engine in the housing. The data capture assembly includes a solid-state imager with an array of photocells or light sensors, and an optical assembly for capturing return light scattered and/or reflected from the target being imaged over a field of view, and for projecting the return light onto the imager to initiate capture of an image of the target. Such an imager may include a one- or two-dimensional charge coupled device (CCD) or a complementary metal oxide semiconductor (CMOS) device and associated circuits for producing and processing electrical signals corresponding to a one- or two-dimensional array of pixel data over the field of view. These electrical signals are decoded and/or processed by a programmed microprocessor or controller into information related to the target being read, e.g., decoded data identifying the target. The controller is operative for transmitting the decoded data, either via a wireless or wired link, to a remote host for further processing, e.g., price retrieval from a price database to obtain a price for the identified target.
For either the moving laser beam reader or the imaging reader, the optical assembly generally comprises one lens, or a plurality of lenses of different optical powers, mounted in a cylindrical lens barrel. For example, in the case of an imaging reader, a classical Cooke triplet may be mounted along an optical axis in the lens barrel. Sometimes, a fourth lens is added to widen the field of view. Although each lens is traditionally made of glass for improved thermal stability, at least one or more of the lenses are typically made of plastic due to the lighter weight and lower molded fabrication cost of plastic lenses compared with glass lenses. The optical assembly comprised of the lens barrel with the lenses mounted therein is installed as a unit into a cylindrical chassis passage formed in a chassis that, in turn, is mounted in the reader. In the case of an imaging reader, the installation enables the captured light to be focused onto the imager.
There are several ways to install the optical assembly in the chassis passage. One way is to press fit the lens barrel in the chassis passage, typically by using crush ribs that are provided either on the outer circumferential surface of the lens barrel, or on the inner circumferential surface of the chassis passage. The crush ribs are radially compressed during sliding insertion of the lens barrel and form an interference fit to hold the lens barrel in place within the chassis. In the case of an imaging reader, the interference fit fixedly positions the optical assembly relative to the imager so that the optical assembly can accurately focus the captured return light onto the imager. Another way is to configure the outer diameter of the lens barrel and the inner diameter of the chassis passage with a sliding interference fit, without using crush ribs. Still another way is to provide threads on the lens barrel and in the chassis passage, and to rotatably thread the lens barrel into the chassis passage. A further way is to twist-and-lock the lens barrel into the chassis passage by first sliding the lens barrel into the chassis passage, and then turning the lens barrel about the optical axis.
A disadvantage of all of these installations is that there is a tendency for debris to be generated when the lens barrel frictionally engages and rubs against the chassis passage. The lens barrel and the chassis can each be constituted of either metal material or synthetic plastic material, and sometimes the lens barrel and the chassis can be coated with a metal plating. Whether it is plastic or metal scrapings from a crush rib compression fit, or an interference fit, or a twist-and-lock fit, or whether it is flakes from a metal plating that has been sheared off, or whether it is particles caused by a rotary threaded fit, all such scrapings, flakes and particles constitute undesirable pieces of debris, which, as experience has shown, has a tendency to fall loose and migrate to optical surfaces of the reader. For example, in the case of an imaging reader, any debris on the imager is especially problematic as the imager does not tolerate foreign debris and can create blemishes in the captured image. In the case of a moving laser beam reader, any debris on the mirrored scan component or on the photodetector is disadvantageous. Such debris contamination degrades the reader's performance.
Accordingly, it would be desirable to prevent any such debris formed during the installation of an optical assembly in a chassis of an electro-optical reader from migrating to optical surfaces of the reader and thereby degrading reader performance.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions and locations of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.
The arrangement and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.